Thursday, January 31, 2013

Bryozoans (phylum Bryozoa) are tiny organisms that mostly live in colonies (except for one solitary species). They are sometimes called moss animals due to the plant-like appearances of many species. In fact, the name "bryozoa" comes from the Greek words "bryon" for moss and "zoon" for animal. The individual bryozoan animal is called a zooid, and it usually lives in a "chamber" called a zooecium, which is basically a protective chitinous or calcareous exoskeleton. The zooecium has an opening (called an orifice), through which the zooid will extend its lophophore, which is essentially a retractable horseshoe-shaped or circular crown of tentacles for filtering plankton and other tiny food particles from the water. Some species may have an operculum covering the orifice.

There are various types of bryozoan zooids, but all colonies will have autozooids, which are responsible for feeding and excretion. Depending on the species, some colonies may have specialised zooids for brooding eggs or for defense purposes.

Most bryozoans are hermaphroditic, meaning they have both male and female reproductive parts. Some species are simultaneous hermaphrodites with both male and female reproductive parts at the same time. Others are sequential hermaphrodites, starting off as males first before becoming females. In species with separate sexes (or dioecious), the colony may be made up of only zooids of the same sex, or both sexes may present. To reproduce sexually, the sperm will be release into the water. For the eggs, some species also release them into the water, while others will capture the sperm using their tentacles to fertilise their eggs and brood them internally. The eggs will eventually develop into free-swimming larvae, which will settle down on suitable substrates and metamorphose into a zooid. The first zooid of a colony is called the ancestrula, and it will reproduce asexually by budding off new zooids to form a colony.

Depending on the species, the bryozoan colonies may be encrusting, plant-like or lace-like. As such, they are often confused with other similar-looking organisms, such as encrusting sponges, encrusting tunicates, hydroids, algae, and leafy corals. It is sometimes possible to differentiate them by looking closely at the surface of the colony, though this may not always be reliable for plant-like species.

I do not personally know anyone who studies the byrozoans in local waters, and hence most of the byrozoans that I have seen are not yet identified. If you are able to identify them or spot any mistakes below, do let me know!

Encrusting Bryozoans

The most commonly seen bryzoans are probably the encrusting ones - they can be easily found under rocks and coral rubble, on pillars of jetties and coastal structures, and even on living organisms such as snail shells, seaweed and seagrass!

Encrusting bryozoans may superficially resemble encrusting sponges and tunicates, but they usually feel hard when you touch them, unlike sponges and tunicates which usually feel a little soft and rubbery.

A closer examination will reveal cell-like patterns, which are the zooecia (or exoskeleton) of the individual zooids.

This dark brown, encrusting bryozoan has zooecia radiating out from the centre of the colony, forming obvious patterns.

The orifices of this translucent white bryozoan appear like small black dots scattered over the surface of the colony.

A closer look at the colony reveals the zooids within the translucent zooecia.

Encrusting bryozoans can be found on living things too. This white encrusting bryozoan, probably a Membranipora sp., can be commonly found appearing as small white patches on the fronds of marine algae, such as the sargassum seaweed featured in the above picture.

The above picture features a Membranipora sp. growing on the fronds of some seagrass leaf blades.

Lace-like Bryozoans

Most of the lace-like bryozoans that I have seen in local waters attach themselves to sea fans, hydroids and sometimes branching sponges. Compared to the encrusting species, they are easier to identify with their lace-like or ribbon-like appearance, though some may be confused with encrusting tunicates. Lace-like bryozoans are usually from the family Phidoloporidae.

This lace-like bryozoan has numerous holes on the colony, giving it a net-like appearance.

A closer look reveals numerous small dark spots, which are the orifices of the zooecia.

This lace-like bryozoan may appear similar to the previous one from afar, but it lacks the numerous holes.

The zooecia appear somewhat rectangular when you look closely.

Plant-like Bryozoans

Plant-like bryozoans have branching colonies, and are often confused with algae and hydroids. Some species may be very difficult to differentiate from hydroids as the zooecia and orifices may not be obvious.

This branching bryozoan (left) is easily mistaken to be a red branching coralline algae (right), and even more so as they may occur in the same area.

Examine it closely, and you will notice that the "stem" appears to be made up of many segments, which are actually the zooecia.

This orange branching bryozoan is also often mistaken to be a hydroid.

The orifices can be seen when you examine the colony more closely as well.

The above bryozoan is found growing on a piece of log on a mudflat. It exhibits a root-like growth-form spreading on the log surface, instead of standing erect.

Tuesday, January 29, 2013

Cnidarians (phylum Cnidaria) are radially symmetrical animals which possess explosive, harpoon-like cells called cnidocytes. Each cnidocyte contains a secretory organelle (cnidae), which can be a nematocyst that discharges a harpoon-like stinger carrying toxins, a ptychocyst that discharges sticky substances, or a spirocyst that discharges lasso-like threads. Hence while cnidocytes are often called "stinging cells", they can perform other functions apart from stinging. The cnidocyte has a fine, hair-like trigger on the outside which activates the discharging mechanism on contact. Many species of cnidarians can give very painful stings upon contact, and some may even be lethal. In fact, the name cnidaria comes from the greek word "knidē", which means "nettle", which is a plant with lots of hollow stinging hairs on its stem and leaves.

The body plan of a cnidarian is very simple, comprising a coelenteron (i.e. the stomach) and a mouth surrounded by feeding tentacles where most of the cnidocytes are usually located. Cnidarians do not have an anus, and hence the mouth performs both functions of ingesting food and extruding waste. They may occur in two forms – a polyp or a medusa.

A polyp houses its stomach in a elongated cylindrical body column. Solitary species usually attached themselves to the substrate with a disc-like structure (called the pedal disc) on one end (called the aboral end) of the body column. The mouth and the tentacles will be located at the opposite end (called the oral end). Colonial species usually lack the pedal disc, but instead the individual polyps living in the colony are usually connected to each other, either directly or indirectly

A medusa has an umbrella-shaped bell (which houses its stomach) with trailing tentacles. Some cnidarians alternate between polyps or medusae in various stages of their life cycles, while other only occur in one form throughout their lives.

Depending on the species, cnidarians either use their tentacles to filter tiny plankton or organic particles from the water (hence they are known as filter feeders), or they may sting and paralyse bigger prey. Many cnidarians harbour the unicellular algae, zooxanthellae, which produce food through photosynthesis and share with the host cnidarians, and in return for shelter and nutrients (waste products of the cnidarians).

Cnidarians can reproduce sexually or asexually. In sexual reproduction (see above picture), they either release their sperm and eggs into the water for external fertilisation, or brood their eggs internally and release the free-swimming larvae into the water later. In asexual reproduction, they clone themselves through budding (a new individual growing out or divided from an existing animal).

Here are some of the major groups of cnidarians that I have seen in Singapore waters.

A) CLASS ANTHOZOA

Anthozoans only have a polyp stage in their life cycles, and hence do not occur as medusae. The major groups of anthozoans I have seen in Singapore include:

1. Subclass Hexacorallia

Cnidarians from this subclass are often called hexacorals. They possess tentacles that come in multiples of six, and here are the major groups found in Singapore.

Order Actiniaria

Sea anemones (order Actiniaria) are solitary hexacorals named after a terrestrial flower, the anemone, due to their flower-like appearance. A sea anemone has a cylindrical body column, and most species have a specialised foot called a pedal disc to attach themselves to hard surfaces or to anchor themselves into soft substrates.

Tube anemones (order Ceriantharia) are solitary cnidarians which superficially resemble the sea anemones, but build and live in mucous tubes made of discharged nematocyst threads, mucus and bits of marine debris. They have two types of tentacles – around the mouth are shorter tentacles (a few centimetres long) which aid in transferring food particles to the mouth, and surrounding the shorter tentacles are much longer ones (can be over 10 cm long) which sting and capture small prey.

Corallimorphs (order Corallimorpharia) are solitary cnidarians which superficially resemble sea anemones, but they usually have an upturned mouth (which may or may not be surrounded by tentacles or pseudotentacles), unlike the former which have inward turning ones. Their internal anatomy, however, are more similar to those of the hard corals, even though they do not secrete a hard skeleton.

Hard corals (order Scleractinia) are hexacorals which have hard calcareous skeletons. They can be solitary or colonial. Each hard coral polyp resides in a calcareous structure called a corallite, and most species can clone themselves into huge colonies stretching many metres, comprising thousands of corallites side-by-side.

Zoanthids (order Zoantharia) are colonial cnidarians which resemble sea anemones clustering together in a colony, and hence they are also called colonial anemones. The polyps are connected at the base by a common fleshy tissue, and there are channels within the common tissue linking the stomachs of the individual polyps.

Cnidarians from this subclass are often called octocorals. They possess feather-like tentacles that come in multiples of eight, and here are the major groups
found in Singapore.

Order Alcyonacea

Soft corals (order Alcyonacea) are octocorals which do not secrete a hard calcareous skeleton, but instead are connected to each other by fleshy tissues, soft spreading membranes or ribbon-like horizontal branches.

Helioporacea corals (order Helioporacea or Coenothecalia) are octocorals that live in a colony supported by a hard aragonite skeleton. In Singapore and the Indo-West Pacific region as a whole, only one species from this order has been recorded - the Blue Coral (Heliopora coerulea). The blue coral got its common name comes from its blue skeleton.

Sea pens (order Pennatulacea) live in colonies exhibiting quill-like appearances. They usually live on soft bottoms, such as sandy or muddy substrates, and are able to burrow into the substrates partially or completely. Unlike most other cnidarians, sea pen colonies are formed from a single large polyp called the oozooid. Secondary zooids then bud off from the sides of the oozooid to form the colony.

Hydrozoans (class Hydrozoa) are cnidarians which may exist either as a polyp or a medusa (more precisely a hydromedusae), or alternate between the two forms. The polyps of some species form plant-like colonies (commonly called hydroids) with chitinous skeletons, while other colonial species may build a hard calcareous skeleton instead. The medusae may be free-living (called jellyfish) or occurs as buds on the surface of the colony.

Scyphozoan jellyfish (class Scyphozoa) are cnidarians which spend the majority of their lives as free-swimming individuals, though most species have a polyp stage in their life cycles too. Unlike hydrozoan jellyfish which usually appear transparent with fine trailing tentacles, many species of scyphozoan jellyfish have coloured, translucent to opaque and thick oral arms.

Sunday, January 27, 2013

Hydrozoans (phylum Cnidaria, class Hydrozoa) are radially symmetrical animals which possess explosive, harpoon-like cells called cnidocytes. Each cnidocyte contains a secretory organelle (cnidae), which can be a nematocyst that discharges a harpoon-like stinger carrying toxins, a ptychocyst that discharges sticky substances, or a spirocyst that discharges lasso-like threads. Hence while cnidocytes are often called "stinging cells", they can perform other functions apart from stinging.

The body of an individual hydrozoan comprises a stomach (coelenteron) and a mouth surrounded by tentacles. They can be solitary or colonial. The above photo shows a colonial hydrozoan with a chitinous skeleton, exhibiting a plant-like appearance. Other sessile colonial species may build a hard calcareous skeleton instead.
Mature hydrozoans may exist either as a polyp or a medusa (more precisely a hydromedusae), or alternate between the two forms. A polyp is sessile, and has a cylindrical body column housing the stomach.

A hydromedusa has an umbrella-shaped bell housing the stomach. Unlike most other cnidarians, the medusae of hydrozoans may not always occur as free-living jellyfish. In many colonial species, they just occur as buds on the surface of the colony for sexual reproduction purposes. And while an individual polyp is sessile, some species form motile colonies that drift on the surface of the water, along with the currents, wind and tides.

Hydrozoans may either feed on plankton by gathering them with their tentacles, or sting and paralyse bigger prey. Many hydrozoans can sting very painfully, and some may result in serious allergic reactions in human, though death cases are rare.

Hydrozoans can reproduce asexually or sexually. The polyps can clone themselves to produce more polyps, or produce medusae by budding. The medusae may be free-swimming jellyfish, or as mentioned earlier, remain attached to the colony in some colonial species. The medusae is the sexually-reproductive stage of the hydrozoans' life cycle, and they have separate sexes. The eggs and sperm are broadcast into the sea for external fertilisation. The fertilised egg develops into a free-swimming larva, and depending on the species, will eventually either settle on a suitable substrate to develop into a polyp and or a medusa. For colonial species, the polyp will clone itself to produce more polyps, and in some species, may build either a chitinous or calcareous skeleton.

The hydrozoans that I have seen in Singapore are mostly from the subclass Hydroidolina. Members of this subclass are commonly called hydroids. Unfortunately, I am unable to identify most of them, as I couldn't seem to find resources on the hydroids of Singapore. If you are able to identify any of those which I couldn't identify or spot any mistake, please do drop me an email!

The hydromedusae, Aequorea spp., are sometimes seen on our shores. They have a glassy transparent appearance, and a shallow furrow is present between the stomach and the margin of the bell. Radial canals, appearing like lines to the naked eye, mark the furrow. Based on Nicholas' and Joo Yong's paper in 2012, tThe above hydromedusa should be Aequorea pensilis, which has up to 160 or more radial canals. Contact with this hydromedusa may result in sharp itchy rashes with light or intense swelling that can persist for several hours.

Lytocarpus spp. are hydroids with feather-like appearances. They are known to give painful stings.

This unknown hydroid species forms pinkish red colonies.

This is yet another unknown hydroid with orange-coloured colonies.

I also could not identify this yellowish hydroid with long and flimsy-looking colonies.

The above unidentified hydroid colony is quite small - about 5cm tall.

From some of the resources I have found online, the whitish, flower-like organisms are likely to be hydroids as well.

This hydroid with yellowish to brownish polyps can be quite abundant on some of our shores.

Thursday, January 24, 2013

Scyphozoan jellyfish (phylum Cnidaria, class Scyphozoa) are radially symmetrical animals which spend the majority of their lives as free-swimming individuals. The body of a jellyfish comprises a gelatinous umbrella-shaped bell housing a stomach (coelenteron) and a mouth surrounded by trailing tentacles. Like other cnidarians, they possess explosive, harpoon-like cells called cnidocytes. Each cnidocyte contains a secretory organelle (cnidae), which can be a nematocyst that discharges a harpoon-like stinger carrying toxins, a ptychocyst that discharges sticky substances, or a spirocyst that discharges lasso-like threads. Hence while cnidocytes are often called "stinging cells", they do perform other functions apart from stinging.

Apart from scyphozoans, other cnidarians such as hydroids and cubozoans also have jellyfish stages in their life cycle.

Scyphozoans may either feed on plankton by gathering them with their tentacles, or sting and paralyse bigger prey with their trailing tentacles. Some scyphozoans can sting very painfully, causing medical problems ranging from minor skin reactions to vomiting in human, and death cases have been reported.

Jellyfish are usually seasonally abundant in Singapore, and sometimes, hundreds can be seen in local waters. It is common to see some stranded on the beach during low tide as well.

Scyphozoans can reproduce sexually or asexually. In sexual reproduction, the male and female jellyfish of most species broadcast their eggs and sperm into the sea for external fertilisation. The females of some species, however, may brood the fertilised eggs. The fertilised egg develops into a free-swimming larva, and will eventually settle on suitable substrate to develop into a sessile form (called a polyp or more precisely, a scyphistoma), where they exist much like sea anemones, attached to the sea floor with their tentacles facing upwards. As the scyphistoma matures, it will either clone itself to form more polyps and each polyp will develop into the jellyfish form (called a medusa, or more precisely, a scyphomedusa for scyphozoan jellyfish), or produces the scyphomedusae by strobilation - a form of asexual reproduction which involves dividing the body into segments, and each segment will develop into a jellyfish.

From a commercial perspective, scyphozoan jellyfish are eaten as a delicacy in many Asian countries. In the wild, many big marine animals, such as sea turtles and some of the bigger fishes, feed on jellyfish.

The few jellyfish that I managed to identify were largely based on the information provided by Dr M. N. Dawson on his websites. Being no scientist, hopefully I got the identity right! If you spot any mistakes, or are able to identify any of those which I couldn't identify, please do drop me an email!

Here is a side view of an Acromitus sp. The bell is more than 10cm wide.

Catostylus spp. also have finger-like oral arms, but lacks the whip-like appendages. The bell is more than 10cm wide.

Family Cassiopeidae

The Upsidedown Jellyfish(Cassiopea sp.) is usually seen with its eight oral arms facing upwards, appearing like a sea anemone. It harbours the unicellular algae, zooxanthellae, which produce food through photosynthesis and share with the host jellyfish, in return for shelter and nutrients (waste products of the host). Since most of the algae are in the oral arms, being upside-down lying on the seabed will expose the algae to more sunlight and hence photosynthesize better.

Here is the Upsidedown Jellyfish with the right-side up. Studies have shown that they can release stingers in a layer of mucus into the surrounding water, and may cause rashes and itchiness if they touch a person's skin.

The colour of the Upsidedown Jellyfish may be green or brown. It can grow to rather big sizes with the bell more than 12cm wide.

Family Mastigiidae

This Mastigias sp. has oral arms with club-shaped extensions. The bell is spotted. I have only seen it a few times in Singapore, and they are usually rather small, with the bell about 5cm or less.

Family Pelagiidae

Chrysaora spp. usually has numerous tentacles attached to the margins of the bell, and several ribbon-like oral arms. Based on a paper published in 2012 by Nicholas Yap and Ong Joo Yong, the species above should be Chrysaora chinensis. It is usually pinkish orange or reddish in colour, has 24 long marginal tentacles, and faint reddish spots scattered evenly on the exterior of the bell. Sometimes called the Sea Nettle, Chrysaora species give very painful stings.

It appears to be seasonally abundant in Singapore, and sometimes hundreds can be seen. The bell can exceed 10cm wide.

Jellyfish I Couldn't Identify

The following are jellyfish which I could not identify using Dr Dawson's websites. If anyone can identify them, do drop me an email!

This white jellyfish appears much like a Chrysaora sp., with the marginal tentacles and ribbon-like oral arms. It's likely to be a related species or variation of the same species. The bell is about 6cm wide.

This bluish jellyfish is sometimes found stranded on our shores. I will estimate the bell to be about 20cm wide.

This purple jellyfish was seen only once. The bell is about 5cm wide.

This huge jellyfish is sometimes seen on our northern shores. The bell is more than 20cm wide.

This is possibly the biggest jellyfish that I have seen in Singapore so far, with the bell about 40cm wide!